#particles {
        position: absolute;
        width: 100%;
        height: 100%;
        background: url('particle.png') repeat 0 0;
        animation: fall 5s infinite linear;
    }
    
    @keyframes fall {
        0% {
            background-position: 0 0;
        }
        100% {
            background-position: 0 100%;
        }
    }
</style>